Day old wild chicken rescue - help

I'm attending school on a very small island with wild chickens running everywhere. Yesterday 2 students found a distressed day-old chick in the woods right at dusk and could not locate the mother. They were going to leave it by a fence, but I happened to walk by and volunteered to take it and made a makeshift incubator out of a desk lamp and cardboard box.The only experience I have is from raising 4 chickens from chicks in the past, so I know a little about them, but need some help.

1) We don't really have agriculture on the island, so there isn't a farm I can take him to or baby chick starter for food. I've made him an organic chicken feed out of Quaker Old Fashioned oats, flaxseed, lentils, yeast, peas, and maple syrup. (There was a recipe online, and I substituted the ingredients as best I could. The island is very small, and we don't have a huge variety of things here). He's also getting a chopped up boiled egg with this, and some pieces of lettuce. Does anyone have some suggestions on how to supply him with grit? should I just find some small rocks? how small? Any suggestions on feed?

2) what about worms/parasites/disease? I saw him pecking at his down, and don't know if he's preening or has something else going on. We don't have a vet visiting the island until the middle of October. Is there anything I should keep an eye out for?

3) Would it be impossible to get a wild hen to adopt him? I've heard about people doing it with their domesticated chickens, but I worry it would kill him if she rejects him. It would be best for him to be raised with the other wild chickens, as I'm only here for 20 months and cannot properly care for him after he gets past the cardboard box stage as I live in an apartment (The landlord is already not loving the chick situation). I'm also worried about people harassing him once he is running about town if he becomes too trusting of people. Should I just raise him as hands off as possible for a few weeks and then set him free when he can keep warm on his own?

4) Chickens are flock animals, and I worry about him being by himself- he cheeps a lot. It would be extremely easy to find another baby chick to catch to keep him company, but I don't really feel like it's ethical to take a chick away from its mother. Would it make it easier to re-introduce him to the wild if he had another chick companion (as opposed to a human companion such as myself? I'd love to carry him everywhere, but it's not in his best interest long-term). Will he be ok if he is alone?

Thanks for any advice or suggestions. I'm absolutely slammed at school, and thought someone might have some ideas to help give him a good shot once he's released him back into the wild.

First of all
You have done a good thing. But i cant help you with much. To get a wild hen to adopt him would be very difficult. She would have to be broody sitting on a nest for her to even attempt to adopt it.

Hands off would be a good idea but i doubt that he would ever be able to survive in the wild after being fed from you. As for food i think you are doing the best you can. Good luck

If he's cheeping excessivly you might want to check the temp. in his box. He might be too cold. As far as him having a companion; try putting in a small mirror or maybe a small stuffed animal. The mirror trick will work for parakeets and I've read about it working for lone chicks. I live in the desert and have used sand from my yard for chick grit. Good job on the feed. You could try putting in things that he would forage for in the wild to help him become familiar with them as a food source. Whatever you see the other wild chickens eating. Maybe a small bug once in a while. I wouldn't be too worried about handling him if you need to, as long as he doesn't become your lap-chicken. Maybe at around 6-8 weeks old, you could release him. Good luck

You are going to kill it with diet as described. If you can not get a chick starter, then work on getting some insects of even ground up seafood in that mix. You are not clear about chick's age although it appears to have been easy to catch so either it is very young or in poor health. An incandescent bulb with box and a rag can be used to keep chick warm.

Just keep the chick warm, dry with the best feed and water you can provide. Do not kill it with too much love.